Solid lubrication offers many benefits over conventional oil-based hydrodynamic and boundary lubrication. Solid lubrication systems are generally more compact and less costly than oil lubricated systems since pumps, lines, filters and reservoirs are usually required in oil lubricated systems. Greases can contaminate the product of the system being lubricated, making it undesirable for food processing and both grease and oil outgas in vacuum precluding their use in space applications. One of the primary goals of a solid lubricant is obtaining low friction.
Polytetrafluoroethylene (PTFE) is known by the trade name TEFLON®. PTFE is well known as a low friction material and has thus received much attention for use as a solid lubricant. It also has other desirable properties including high melting temperature, chemical inertness, biocompatibility, low outgassing and low water absorption. However, PTFE wears much more rapidly than most other polymers preventing its use as a bearing material in most cases.
A variety of solid lubricant applications require low cost solid lubricants. Epoxies are generally producible at low cost, and are easily formable into a variety of shapes. Although generally not lubricious in neat form and having a poor friction coefficient and wear resistance, epoxy-based composites can provide reasonable tribological properties by adding certain fillers, such as TiO2, SiO2, Al2O3, and Si3N4.
Some of the present inventors have disclosed low cost composite coatings consisting of PTFE and Epoxy which provide a 100× improvement in wear resistance as compared to either of its constituents alone and reduced friction coefficient. (See N. L. McCook, D. L. Burris, G. R. Bourne, J. Steffens, J. R. Hanrahan & W. G. Sawyer “Wear Resistant Solid Lubricant Coating Made from PTFE and Epoxy” Tribology Letters, Vol. 18, No. 1, Jan. 2005). The discussed coating is made by impregnating an expanded PTFE film with epoxy. Although the disclosed Epoxy/PTFE composite provides a good combination of wear resistance and friction coefficient, low cost wear resistant lubricious composites having higher wear resistance and friction coefficient are desired for many applications.